Hard things make us better. It’s what we were designed for. If you doubt this, ask: why does my body - as if by magic - adapt to these hard things? When I lift a weight repeatedly I will be able in a few days to do that more easily. This is a good thing to know.
What are some hard things worth trying? Here’s two that have impacted me:
Running “the mile”. I joined the Brown running team in a parking lot. They were doing a timed mile. I was curious, so I joined. This was among the hardest things I can remember doing. You might think running a mile is easier than, say, 5 miles. But you’d be wrong. The reason is that a hard mile - an all-out effort - maximally stresses two systems at once: aerobic AND anaerobic.
The cold plunge/ice-bath shares with the mile that it stresses two systems at once: the physical and the mental. If you don’t have an ice-bath at home, try a cold shower. Regardless, the steps are the same: you need to convince yourself to do it in theory; then you need to convince yourself to actually go in; and then to stay…just a bit longer!